Not applicable
1. Field of the invention
The present invention relates to a method and an apparatus to improve the internal quality of a continuously cast steel section and, more particularly, to mechanically vibrate a solidified shell of such a steel section at a site upstream of the end of a contained liquid steel core consisting of high carbon steel or alloy steel to reduce segregation by dispersing carbon or alloying elements during final solidification of the liquid core.
2. Description of the Prior Art
Inherent internal conditions in the process of continuous casting of steel sections such as billets, blooms, rounds and slabs have a significant influence on the internal quality of the steel section especially when casting high carbon steel and alloy steel. The inherent conditions are center looseness, center segregation, and equiaxed grain ratio. While center looseness and center segregation are not desirable, obtaining an equiaxed grain ratio is very desirable. Several methods of combating or enhancing the above mentioned conditions are known to produce a varying degree of success. Two such known methods are electromagnetic stirring and soft reduction. Electromagnetic stirring is accomplished by applying a magnetic field to the cast section liquid core to agitate the steel causing the breakage of the dendrite tips and dispersion of inclusions. This action promotes recrystallization in the solidification process and minimizes center segregation. The soft reduction method involves progressively squeezing a mushy zone in the solidifying section to refine the grain size at the center of the section, which also influences center segregation and center looseness. Electromagnetic stirring and soft reduction methods are capital intensive, when initially installing the necessary equipment into a new facility or when retrofitting the necessary equipment into an existing facility.
It is an object of the present invention to provide a method and an apparatus to introduce vibration by physically impacting a continuously cast section at a location before final solidification.
It is a further object of the present invention to provide a method and an apparatus to apply mechanical vibrations to an outer shell of a continuously cast section to vibrate an internal mushy zone sufficiently to cause the breakage of dendrite tips and thereby promote recrystallization and to enhance refinement of the grain structure by dispersion of segregated carbon or alloying elements, to produce an equiaxed and dense structure, and to reduce porosity by facilitating the floatation of gas bubbles to the top of the mold.
According to the present invention there is provided an apparatus for reducing segregation in a solidifying section with a contained liquid core during casting of a continuous metal strand of high carbon steel or alloy steel, the apparatus including the combination of at least one hammer having a face surface for engaging a solidified shell enclosing a liquid steel core having concentrations of carbon or alloying elements, a vibrator having an operating frequency of between 1000 and 6000 cycles per minute coupled to the hammer for vibrating the liquid core to disperse concentrations of carbon or alloying elements during solidification of the liquid core, a dead weight mass mechanically coupled to the hammer for maintaining a desired contact force on the solidified shell by the hammer while vibrated by the vibrator, and guides for stabilizing the hammer.
The present invention further provides a method for reducing segregation in a solidifying liquid core during casting of a continuous metal strand of high carbon steel or alloy steel, the method including the steps of, selecting a site along a cast strand upstream of the end of a liquid core contained within a solidified shell of a continuous casting installation for high carbon steel or alloy steel, and vibrating the solidified shell at the site at a frequency selected to disperse concentrations of carbon or alloying elements during solidification of the liquid core to refine the grain structure during solidification of the liquid core. Preferably, the solidified shell is vibrated at a frequency of between 1000 and 6000 cycles per minute.